Shane Gowland

This plugin adds support for Topic Thumbnails with bbPress. It works by retrieving the first image from each topic and displaying it alongside the topic title on the index page. Thumbnails are sized according to the default ‘thumbnail’ size in your WordPress media settings. The images will also resize appropriately if you’re using a responsive WordPress theme.
This plugin works with GD bbPress Attachments and most other bbPress image management plugins.
If you enable this plugin while bbPress is disabled (or not installed) it will display a warning message.

bbPress Topic Thumbnails

Provides bbPress with support for topic thumbnails.

normen

Shows a label for unread forum posts. Marks topic as read when user visits the topic. 
A “mark all read” button on each page allows setting the topics on that page as unread. 
Based on a plugin by 3sixty, however not much code is left of it 😉

bbPress Topic Thumbnails vs BP Unread Posts